Integrated Experimental and Modeling Study of Geochemical Reactions of Simple Fracturing Fluids with Caney Shale

Abstract

Interactions between rock minerals and hydraulic fracturing fluids directly impact the geochemical and geomechanical properties of shale formations. However, the mechanisms of geochemical reactions in shale unconventional reservoirs remain poorly understood. To investigate the geochemical reactions between shale and hydraulic fracturing fluids, a series of batch reactor experiments were undertaken. Three rock samples with different mineralogical compositions and three fluid samples of different compositions [deionized water, deionized water + 2% potassium chloride (KCl), and deionized water + 0.5% choline chloride (C5H14ClNO)] were used. Experiments were undertaken at reservoir temperature and atmospheric pressure. Elemental compositions of effluents after 1, 3, 7, 14, and 28 days were analyzed using inductively coupled plasma mass spectrometry. Medical computed tomography scanning and X-ray fluorescence spectroscopy were conducted on the entire core to help upscale results obtained from rock–fluid interaction experiments. Geochemical modeling using a reactive simulator, TOUGHREACT, was undertaken to corroborate experimental results. Results show that a lower pH triggered high dissolution rates in the rock samples, especially the carbonate components. As the pH increased, the rate of dissolution declined significantly, though for most cases dissolution still continued. The observed dissolved silica concentrations were much higher than the quartz solubility, suggesting that much of the silica originated from more soluble silica polymorphs and possibly desorption from clay mineral exchange sites. The concentration of most elemental species in solution increased, but aluminum (Al) and magnesium (Mg) concentrations declined rapidly following initial entry into solution. Geochemical modeling corroborated the conclusions regarding mineral dissolution and precipitation observed from experiments, notably the dissolution of calcite and pyrite in the reacted shale samples, the likely presence of silica polymorphs such as opal, chalcedony, or amorphous silica in these samples, and the reduction of Al and Mg concentrations in solution by precipitation of secondary aluminosilicate phases. The de-flocculation of clay minerals during reaction implies fines migration after hydraulic fracturing. This is detrimental to reservoir productivity as clay fines are displaced and lodged within the micro- and nanofractures created during fracturing. The immediate consumption of Al and Mg also has implications on blockage of hydrocarbon pathways due to precipitation of new minerals in these locations.

Mineral and Fluid Transformation of Hydraulically Fractured Shale: Case Study of Caney Shale in Southern Oklahoma

“…6) after reacting with rock powders. This trend is consistent with previous published works where synthetic fracturing uids were used (Awejori et al 2022). Decreased Mg concentration can be attributed to precipitation of new minerals, exchange in clay interlayer or re-adsorption to clay sites.…”

“…Reaction with produced brines caused mineralogical changes in the samples as seen in Fig. Compared to previous experiments (Awejori et al 2021(Awejori et al , 2022, the mineralogical changes in this experiment were much slower and subtle, which would be expected given that the reacting uid is a produced brine, thus a uid that has reacted (at least to some extent) with the shale formation. Based on previous experimental and modeling work (Awejori et al 2022), reactions in this experiment are believed to proceed in the following order.…”

“…Compared to previous experiments (Awejori et al 2021(Awejori et al , 2022, the mineralogical changes in this experiment were much slower and subtle, which would be expected given that the reacting uid is a produced brine, thus a uid that has reacted (at least to some extent) with the shale formation. Based on previous experimental and modeling work (Awejori et al 2022), reactions in this experiment are believed to proceed in the following order. Breakdown of pyrite is initiated by dissolved oxygen in the reacting uid, which leads to the generation of transient and localized acidity by the oxidation of the sul de in pyrite to sulfuric acid.…”

Creep Properties of Shale and Predicted Impact on Proppant Embedment for the Caney Shale, Oklahoma

“…Each of these mineral groups has different mechanical and chemical stability which could potentially be taken out of equilibrium because of drilling, completions and production (Awejori et al, 2022 andXiong et al, 2022). Organic matter is not detectable in the XRD but the SEM micrographs and the EDS chemical elemental maps show the difference in the amount present as well as in the morphology of kerogen, which is present in ductile zones as fine grained and well dispersed, compared to the larger lens-like shapes of kerogen in reservoir zones with a sponge-like texture indicating kerogen porosity.…”

Comparative Laboratory Study of the Geochemical Reactivity of the Marcellus Shale: Rock–Fluid Interaction of Drilled Core Samples vs. Outcrop Specimens

“…The biggest volume of flowback water occurs shortly after the fracturing is completed and the well is prepared for production [9]. Reactions occur between the formation and the injected fluids, causing mineral dissolution and the precipitation of new minerals, which might have an impact on the reservoir's petrophysical properties [10]. Most of the Marcellus and other northeastern US formations are fractured in horizontal wells.…”